1. Field of the Invention
This invention relates to a twist drill. More particularly, this invention relates to a twist drill having a tool body including helical flutes in the outer peripheral surface of the tool body to smoothly discharge cuttings chips and provide improved rigidity against cutting resistance.
2. Description of the Related Art
A conventional twist drill comprises a cylindrical tool body provided with at least one helical flute and land, wherein the flute and the land follow a helical angle to a forward cutting point. The rearward end of the tool body of the twist drill is securable in a chuck; for example, of a hand tool, or a drilling machine. The cutting point of the drill is of generally conical-shape, with a cutting edge from which a pair of diametrically opposed cutting edges defined by the leading faces of the fluted lands and the flanks of the drill point that form the end faces of the fluted lands. The outer periphery of each fluted land has at its leading edge a radial projection which is variously termed a land, a cylindrical land, and a support margin. These two support margins extend along the length of the fluted lands.
The design of the flute of the twist drill is extremely critical to its performance. The design of the flute determines the ability of the twist drill to form, accommodate, and evacuate chips produced during the cutting operation, thus carrying away heat.